Self-triggered blocking oscillator



1954 E. F. M NICHOL, JR., ET AL 2,697,166

SELF-TRIGGERED BLOCKING OSCILLATOR Filed Oct. 10, 1945 s Sheets-Sheet 1 TIME INVENTORS ARDEN H. FREDRICK EDWARD F. MACNICHOL JR.

ATTORNEY 4, 1954 E. F. M NICHO JR.. ET AL 2,697,156

SELF-TRIGGERED BLOCKING OSCILLATOR 3 Sheets-Sheet 2 Filed Oct. 10, 1945 FIG.5

JIHHFIFIII E} NORMAL BIAS FIG.6

OUTPUT INVENTORS ARDEN H. FREDRICK EDWARD F. MACNICHOL JR.

CIRCUIT WIDE GATE ATTORNEY Dec. 14, 1954 E. F. M NICHOL, JR. ET AL SELF-TRIGGERED BLOCKING OSCILLATOR Filed Oct. 10, 1945 3 Sheets-Sheet I5 0 F|G.8 i A U B H I TIME FIG.|O

INVENTORS Cg dd g D M ATTORNEY United States Patent SELF-TRIGGERED BLOCKING OSCILLATOR Edward F. MacNichol, Jr., Hamilton, and Arden H. Fredrick, Boston, Mass, assignors, by mesne assignments, to the United States of America as represented by the Secretary of the Navy Application October 10, 1945, Serial No. 621,575

16 Claims. (Cl. 250-27) This invention relates to voltage pulse-forming circuits, and more specifically to voltage pulse forming circuits which are capable of producing a series of very short duration voltage pulses equally spaced in time sequence.

Circuits such as multivibrators or blocking oscillators have been used to produce a series of voltage pulses, depending on the exponential discharge of a condenser through a resistance to control the time spacing between these pulses, but slight variations in the circuit constants or bias voltages cause variations in the pulse spacings.

A primary object of the present invention is to overcome this difficulty, for which purpose we employ an accurate delay network, a portion of the output voltage pulse being delayed in the delay network and then used to initiate the operation of the succeeding cycle. In this way, we obtain a succession of rectangular voltage pulses of substantially equal time spacing.

We have found that even with a delay network for timing the spacing of the first few pulses may not correspond to the spacing between the following pulses be cause the bias on the grid of the tube is varying. A more particular object of the present invention is to eliminate this unequal spacing of the pulses. This is done by providing a means, preferably an electron tube, which means becomes conductive between pulses, and so discharges the potential on the capacitors of the circuit, and thereby restores the grid of the oscillator tube to normal bias.

The operation of the circuit is initiated by a wide gate, and inasmuch as the rise of the gate may be relatively slow, the first pulse generated may not coincide with the initiation of the trigger voltage, or may not have the square shape of the succeeding pulses. A further feature and object of the invention is to counteract this difiiculty, and to this end the trigger voltage which initiates the wide gate is also employed to force the first pulse or zero marker, and to make the same relatively independent of the shape of the leading edge of the gate.

To accomplish the foregoing general objects and other objects which will hereinafter appear, several forms of the invention are more particularly described in the following specification. The specification is accompanied by drawings in which:

Fig. 1 is a circuit diagram of a pulse forming circuit using a delay line;

Fig. 2 is a modification;

Fig. 3 shows voltage-time curves explanatory of the operation of the circuits shown in Figs. 1 and 2,

Fig. 4 is a circuit diagram of a modification embodying features of our invention;

Fig. 5 shows voltage-time curves explanatory of the operation of the circuit shown in Fig. 4;

Fig. 6 shows a modification of Fig. 4;

Figs. 7 and 8 show voltage-time curves explanatory of the operation of the circuit of Fig. 6, respectively with and without the forcing action of the trigger voltage;

Fig. 9 is a voltage-time curve illustrating the operation in the absence of a clamping tube; and

Fig. 10 shows the operation with a clamp tube.

Referring to the drawing, and more particularly to Fig. 1, the pulse forming line 17 is connected across the secondary 14 of a blocking oscillator transformer 11. When the wave front initiated by the blocking oscillator reaches the open end of the delay line 17', it is reflected back to the transformer and upon its return initiates the next pulse of the blocking oscillator.

Considering the circuit in detail, thermionic tube 1 has Patented Dec. 14, 1954 "ice a plate 2, a screen grid 3, a control grid 4, and a cathode 5. The control grid 4 is connected through the grid resistor 6 to a source of bias potential indicated at 18, and also to the control grid 22 of a thermionic tube 20 which is connected as a cathode follower. The grid 4 is also connected through the winding 12 of the transformer 11 and condenser 10 to ground. The transformer 11 is preferably an iron core transformer which is capable of reproducing rectangular or square pulses of short duration, say of the order of a microsecond.

The suppressor grid 3 of tube 1 is normally maintained sufliciently negative to prevent conduction of the tube 1 by the potential applied to this grid from the point 17 through the resistance 7. A multivibrator or other device capable of producing rectangular pulses of positive voltage and predetermined time duration and repetition rate is connected at 9 and is coupled to the screen grid 3 by means of the coupling condenser 8. When the screen grid 3 is driven sufliciently positive by the voltage applied at 9, tube 1 begins conducting, the flow of plate current through the winding 13 inducing a voltage in Winding 12 of such a polarity as to cause the control grid 4 to be driven positive. This initiates operation of the blocking oscillator. Should the bias potential at 18 be positive enough with respect to the cathode 5 so that conduction would begin again in tube 1 after the potential of the control gn'd 3 had risen by means of the discharge of condenser 10 through the resistor 6 to a point beyond the cutoff voltage, the circuit would again regenerate, the above described action being repeated, thereby producing a series of successive pulses, spaced an amount determined by the RC product of condenser 10 and resistance 6, and continuing in operation during the period of the wide gate applied to the screen grid 3. But such as action would be subject to unequal spacing of pulses due to slight variations in circuit constants or bias potentials, and would therefore not be satisfactory if high precision is desired.

To accurately determine the time interval between successive pulses from the blocking oscillator, there is employed a transformer winding 14, and a delay network or artificial transmission line 17' containing inductances 15 and condensers 16. The mutual coupling between windings 14, 12 and 13 causes a voltage pulse, corresponding to the output voltage of the blocking oscillator, to be induced in winding 14, and thereby be applied to the artificial line 17. The network 17 is open-circuited at the far end, so that any voltage pulses upon reaching the end are reflected back without a polarity reversal. The time required for a voltage pulse from winding 14 to travel the length of the network 17' and be reflected back to 14 depends on the values of the constants 15 and 16. The delay network 17 need not be of the specific type shown, but may be of any suitable configuration and contain any desired number of sections.

Since the voltage pulse applied to the network 17 by the winding 14 is reflected from the open end of this network with the same polarity, this reflected pulse will induce a voltage into windings 12 and 13 of the same polarity as existed during the formation of the pulse in winding 14. This voltage pulse on the grid 4, whose potential after the initial cycle of operation has been approaching the bias potential of 18, causes tube 1 to again conduct, thereby forming a pulse as explained previously.

The RC values must be so chosen that the reflected pulse returns before the bias decays far enough toward the bias potential at 18 to allow the tube to refire, i. e. the free period must be slightly longer than the effective length of the delay line.

The tube 20 is a cathode follower, and acts as a buffer between the pulse-forming circuit and the load to which the pulses are applied. It has the usual cathode resistor 25, coupling condenser 27, and grid leak resistor 24, the output being taken off at 26. The coupling condenser 27 is shown connected to the control grid 4 of tube 1, but it may instead be connected to one end of the winding 14. At either point a positive output is obtained, as is necessary for satisfactory operation of a cathode follower of the type shown.

Referring now to Fig. 2, the pulse forming line 40 is terminated by a resistance 41 which is equal to the characteristic impedance of the line. When the wave front initiated by the blocking oscillator reaches the end of the delay line 40, it is entirely dissipated in the resistance 41, and the voltage occurring across this resistance is transferred to tthe control grid of the pentode tube to initiate the next pulse. The duration of each pulse it determined by another delay line 41. Either of these changes may be used independently of the other.

Considering the circuit in detail, the thermionic tube 30 has a suppressor grid 31, a screen grid 32, control grid 33, cathode 34, and anode 35. A bias potential indicated at 44 is applied to the grid 33 through the resistance 37. Condenser of the circuit of Fig. 1 has been replaced by a suitable network or delay line 41, which is similar to the network 17', but designed for a shorter time delay. The screen grid 32 is connected to a source of positive potential at 45 through resistance 36 and is provided with a by-pass condenser 29; The periods of operation of this circuit are controlled by the application of a potential to the suppressor grid 31 from a source indicated at 46, and coupled to the grid .31 through condenser 39. A negative bias potential at 47 connected to grid 31 by the resistance 38 maintains this grid at a negative potential of sufficient amount to keep tube 30 non-conducting when no input voltage is applied at 46. The input voltage at 46 is preferably of a wave form as shown at A in Fig. 3, and must be of sufficient amplitude to raise the grid 31 to a potential at which the tube will start to operate.

Because the impedance 41 connected across the end of network 40 is equal to the characteristic impedance of the network, there is no reflection from the end of the network, but the voltage across the resistance 41 is coupled by means of a coupling condenser 42 to the grid 33.

The bias potential 44 on the grid 33 is of such a value that. when the suppressor grid 31 is raised by the input voltage at 46, the tube 30 will begin conducting. By means of the coupling between the plate winding 13 and the grid winding 12, the flow of plate current causes the grid 33 to be driven positive, thereby increasing the plate current flow, the action being regenerative. While the grid 33 is positive, electrons flow from the cathode 34 to the grid 33 and accumulate on the condensers of the delay line 41, thereby causing the sides of the condensers connected to the grid 33 to assume a negative potential.

The initial negative pulse applied to the delay line 41 when the plate current begins flowing is reflected from the open end of the network and is impressed on the grid 33 after a delay determined by the constants of the network 41. This reflected negative pulse, superposed on the negative potential developed on the condensers of network 41, drives the grid 33 sufiiciently negative to prevent further regeneration, the tube 30 therefore cutting off. The accumulated charge on the condensers of network 41 must. discharge through resistance 37, the time constant of this discharge path being equal to the product of resistance 37 and the total capacitance of the a network 41.

Simultaneously with the beginning of conduction of tube 30, a voltage pulse begins traveling down the delay network 4-0, and upon reaching the terminating resistance 41' is dissipated, the positive voltage pulse at resistance 41' being applied through condenser 42 to the grid 33. If the potential of the grid 33 has risen sufficiently near the bias potential at 44 by the discharge of the condensers of network 41 through resistance 37, this positive voltage pulse from the coupling condenser 42 will cause the tube to again begin conducting and repeat the, cycle of operation.

The negative. voltage on the grid 33 caused by the accumulation of electrons on the condensers of network 41 must have sufliciently discharged through resistance 37 so that the voltage pulse through. condenser 42 from the network 40 will drive the grid 33 positive enough to cause the cycle to repeat.

The thermionic tube is shown connected as a cathode follower in the same manner as in Fig. 1, except that the input through the coupling condenser 27 is obtained from winding 14. of transformer 11. The input to this tube. 20 may also be obtained from the control grid 33, as shown in Fig. 1. The output pulses obtained from the cathode follower at the point 26 Will be of positive polarity, and substantially rectangular in shape.

Fig. 3 shows the Wave forms of various voltages in the circuit of Fig. 1., drawn to the same, time base, scale. Curve Aisthe; voltage applied, to the screen grid f tube 1 which initiates the operation of blocking oscillator,

B represents the output pulses at point 26, and C is the variation of potential of the condenser 10. The flow of electrons from the cathode to the grid of tube 1 causes a slight deviation in bias potential of this grid 3 from that fixed by the D. C. potential at point 18. This is caused by the failure of condenser 10 to discharge completely between pulses to the bias potential of 18, indicated as Normal Bias in Fig. 3. Thus the average bias increases more negatively with each output pulse until a balance is reached between the amount of charge collected on the condenser 10' during the pulse and the amount of charge leaking off through resistance 6 between pulses. This slight change in bias has the detrimental effect of causing the spacing between the first several pulses to be greater than between those formed after this equilibrium bias condition. has been reached since the line pulses have a finite positive slope. This is shown in curve B of Fig. 3, where the time spacing between the output pulses increases until the constant value T3 is reached.

Fig. 3 will also apply to the circuit of Fig. 2, the curve A representing the voltage applied to the suppressor grid 31 of tube 30, the curve C being the variation in potential of the condensers 48 of the delay network 41 caused by the electron flow from the cathode 34 to the grid 33 of tube 30.

In Fig. 4 an arrangement is shown for eliminating the unequal spacing of the first few pulses, and this constitutes a prime feature of our invention. Here the input circuit of a tube is connected across the end of the delay line which is connected to the transformer winding 14', the arrangement being such that the leading edge of the pulse from the blocking oscillator after being delayed in the line reaches the grid of the tube as a positive pulse, thus causing this tube to become conductive. The flow of current in tube 65 restores the grid of the pentode tube to the normal grid bias.

Considering the circuit of Fig. 4 in detail, the suppressor grid 52 of the tube is normally maintained at a sufiiciently negative potential from a source at 58 through resistance 57 to prevent the tube from conducting. The anode 51' is connected to a source of positive D. C. potential through the transformer winding 12, the screen-voltage-dropping resistor 60 and by-pass condenser 61 being connected to the screen grid 53 in the usual manner. Bias potential to the control grid 54 is supplied from a source indicated at 72 through resistance 69 and transformer winding 14. Connected to the bias potential at point 72 is the anode 66 of tube 65, the control grid 67 of this tube being connected through resistance 64 to one end of the series inductances of delay network 62, the cathode 68 being connected at the junction of condensers 86, resistance 69, and condenser 70. The other end of the series inductances 85 is connected through resistance 63 to one side of transformer winding 14. One end of winding 13 is at ground potential, and the other end is connected to the cathode 77 of tube 74- and thence to ground through potentiometer 78. The slidingcontact 79 connects to the output terminal indicated at 80. The control grid 76 is connected to. a source of negative bias potential at 87 through resistance 81 and through coupling condenser 82 to the secondary of transformer 83.

In Figs. 1 and 2 the pulses are initiated by a gate circuit, and since the rise of the. gate may be relatively slow, the first pulse generated may not coincide with the initiation of the trigger voltage. A second prime feature of our invention counteracts this difficulty, as follows. Simultaneously with. the. application of the gate (F in Fig. 5 and B in Fig. 7) at 59 (Fig. 4) to cause tube 50 to begin conducting, a voltage pulse (G in Fig. 5 and A in Fig. 7) is applied at 84' (Fig. 4) to transformer 83. This may be the same trigger that initiates the gate. Through condenser 82 this voltage pulse raises the potential of the grid 76, causing a rapid increase in plate current in tube 74. This current flow through the cathode resistance 78 raises the potential of the cathode 77, thereby applying a positive voltage pulse on the transformer winding 13. Since. winding 14 is coupled to winding 13, a positive voltage pulse is also applied to the grid 54. The application of this positive voltage pulse to the grid 54 simultaneously with the positive voltage on the suppressor grid 52 insures a rapid. beginning of conduction in tube 50. This additional voltage pulse on the grid 54 is not 1 necessary, but improves the action of the circuit at the beginning of the first pulse.

The polarity of the volts 3e pulse applied at 84 depends on the manner in which the primary and secondary windings of transformer 83 are connected. The condition that must be met is that the grid 76 of tube 74 be driven positive by the voltage applied at 84.

After the tube 50 begins conducting and an output pulse is produced by the blocking oscillator action previously described, a voltage pulse corresponding to the output pulse produced in winding 12 of transformer 11 is induced into windings 13 and 14 by means of the close coupling be tween the windings of this transformer. Winding 13 now serves as the output winding, the voltage induced in it appearing across the resistor 78. By means of the sliding tap 79 the amplitude of the output pulse at 80 may be controlled. The voltage pulse induced in winding 14 traverses the network 62 through series resistance 63, then reaching the termination of the network 62, which is the grid to cathode resistance of tube 65 plus series resistor 64. If the pulse is of such a polarity as to cause the grid 67 to be positive with respect to the cathode 68 tube 65 will conduct, allowing the negative charge on condenser 70 which accumulated during the time the grid 54 of tube 50 was positive to discharge to the bias potential at 72 through the low impedance of the tube 65. This rapid discharge of condenser 70 returns the grid 54 of tube 50 to its normal bias potential during theinterval between output pulses, thereby overcoming the slight variations in pulse spacing caused in the circuits of Figs. 1 and 2 by the change in the control grid bias.

Resistance 64 is of such a magnitude that the sum of its resistance and the grid-to-cathode resistance of tube 65 during the time the grid 67 is positive with respect to the cathode 68 is greater than the characteristic impedance of the network 62. This terminating impedance for the network 62 is desired to insure a reflected voltage wave whose polarity is the same as the incident voltage wave from winding 14. This reflected wave after being further delayed through the network 62 causes the cycle 'of operation to repeat by driving the grid 54 of tube 55 positive by means of the direct connection between this grid and the transformer winding 14. Resistance 63 plus the impedance of winding 14 must also be greater than or equal to the characteristic impedance of the network 62. If this were not true, the reflected wave would be an outputpulse from the winding 14 caused by the blocking oscillator action, the two voltage pulses of opposite polarity causing considerable distortion of the resultant The pulse output generated by the circuit is shown by curve D in Fig. 5.

The circuit of Fig. 6 is very similar to that of Fig. 4, although the diagram has been rearranged. The tube 102 corresponds to the tube 65; the resistor 109 to the resistor 69; the condenser 110 to the condenser 70; the transformer 116 to the transformer 83; the relay line 107 to the delay line 62; the tube 103 to the tube 74; voltage dividef 117 to the divider 78. In Fig. 6 the trigger pulse is shown connected by a lead 115, whereas in Fig. 4 this lead is omitted, but would be connected to the terminal 84.

Fig. 6 differs from Fig. 4 in using a distributed line 107, instead of a lumped line as shown in 62, and in using a phase corrrecting network 111.

The operation of Fig. 6 may be reviewed briefly with reference to Figs. 7 through (although these figures are also applicable to the operation of the circuit shown in Fig. 4). The first pulse. is forced by means of an inverted trigger voltage as obtained from the output of the cathode follower 103 (Fig. 6) and applied through lead 106 to the winding 104 of the transformer in the plate circuit of the pentode 101.

Fig. 7 illustrates the operation of the circuit without Curve B shows the gate with its slowly rising leading edge. Curve C caused by the gate slope.

' 6 shows the output pulse, with the sloping leading edge Fig. 8 illustrates in'contrast, the operation with the forcing action of the trigger voltage. Curve A shows the trigger, and curve B shows the gate, the same as in Fig. 7. Curve C shows the output pulse, which now has a sharp rise.

The negative grid bias on the pentode tube 101 (Fig. 6) limits the blocking oscillator action, so that without the delay only one pulse would be generated for each trigger. All subsequent pulses are derived from their predecessors owing to the action of the delay line, symbolically shown at 107. The first positive pulse on the grid of tube 101 travels to the end of the delay line where it is reflected in phase, since the terminating impedance is made greater than the characteristic impedance of the delay line. This reflected pulse upon reaching the grid of the pentode tube 1 triggers the blocking oscillator for the next pulse, and the action continues as long as the positive wide gate is applied to the suppressor grid.

The resistor 108 increases the impedance seen by the reflected pulse looking from the delay line into the blocking oscillator. When this impedance is equal to or greater than the characteristic impedance of the line, the refiection from the sending end (at the blocking oscillator) is in phase with the generated pulse, and the pulse spacing is made uniform. If this impedance is smaller than the characteristic impedance, partial cancellation of the two pulses occurs, and the ideal spacing is destroyed.

The trigger voltage needed to fire the oscillator depends on the bias. Since this firing of the oscillator depends on the recovery time of the RC circuit 109, 110 the bias can never return to its initial value at the first pulse through natural decay. The pulses are then spaced as shown in Fig. 9. The drops A, C, and E in Fig. 9 correspond to the pulses. The spacing at B, D, and F between pulses is not uniform.

To eliminate this unequal spacing the bias is clamped by means of the triode 102 (Fig. 6). The pulse arriving at the end of the line network turns the clamp tube 102 on so that it conducts freely and provides a low resistance discharge path from the condenser 110. Fig. 10 shows the condition with the bias clamp, the line H representing the normal bias. In this case the spacing between pulses is uniform. It might be expected that the plate of the tube 102 (Fig. 6) should be returned to the lower end of resistor 109, but by returning it to ground, as shown, more stable operation may be obtained.

The phase correcting network 111, is incorporated to improve the frequency response of the delay line. It reestablishes proper phase relation between the higher and lower frequency components passed through the delay line. This restores the sloping front edge of the pulse to a substantially correct front. The resistance 112 in series with the grid lead of the tube 102 provides a high terminating impedance for the line.

The tubes 65 and 102 respectively in Figs. 4 and 6 might be called a switch diode or a triode clamp. A triode is used instead of a diode because the tube must be non-conducting until the pulse reaches the end of the In Figs. 4 and 6 the condensers 70 and 110 respectively build up a high negative charge. This is what makes it possible to have a negative polarity on the anode of tube 65, and to ground the anode of tube 102, because the high negative charge built up on the condenser makes the c'ath ode negative relative to the anode, and so makes the tube conductive.

It is believed that the construction and operation, as well as the advantages, of the improved pulse forming circuits of the present invention, will be clear from the foregoing description thereof.

It will be understood that the output voltage pulse may be taken from the circuit in a dilferent manner than described above, as for example, across a resistor in series with the cathode of the blocking oscillator tube.

It will therefore be apparent while We have shown and described our invention in several preferred forms, changes may be made in the circuits disclosed without departing from the spirit of the invention, as sought to be defined in the following claims.

We claim:

1. In a blocking oscillator circuit comprising a tube having regeneratively coupled grid and anode circuits, and a delay line in one of said-circuits for determining the time repetition rate of the pulses, a bias clamping means for restoring the bias of the tube between pulses, said clamping means including a tube and a resistance-capacitance circuit connected at the open end of the delay line and so arranged that the tube becomes conductive and discharges the capacitors of the delay line and the resistance-capacitance circuit between pulses in order to restore the bias of the blocking oscillator tube.

2. In a blocking oscillator circuit comprising a tube having regeneratively coupled grid and anode circuits, a delay line in one of said circuits for determining the time repetition rate of the pulses, means to apply a switch voltage or wide gate to the tube to control its operation, and a means to apply a trigger pulse to said regeneratively coupled grid and anode circuits at the initiation of the first blocking oscillator pulse whereby the first pulse or zero market pulse is caused to have a substantially vertical leading edge even if the control gate has a sloping leading edge, said last-mentioned means including a cathode follower tube also coupled to said grid and anode circuits to the grid of which the trigger pulse is applied.

3. In a blocking oscillator circuit comprising a tube having regeneratively coupled grid and anode circuits, a delay line in one of said circuits for determining the repetition rate of the pulses, and means to apply a switch voltage or wide gate to the tube to control its operation, a bias clamping means for restoring the bias of the tube between pulses, said clamping means including a tube and a resistance-capacitance circuit connected at the open end of the delay line and so arranged that the tube becomes conductive and discharges the capacitors of the delay line and the resistance-capacitance circuit between pulses in order to restore the bias of the blocking oscillator tube, and additional means to apply a trigger pulse at the initiation of the first blocking oscillator pulse in order to square up the first pulse even if the control gate has a sloping leading edge, said means including a cathode follower tube also coupled to said grid and anode circuits to the grid of which the trigger pulse is applied.

4. A blocking oscillator circuit for producing pulses equally spaced in time sequence comprising, a tube having at least a grid and an anode, means for regeneratively coupling said grid and anode circuits, pulse delaying means in one of said circuits for determining the time repetition rate of said pulses, the output of said delay line being coupled to the other of said circuits through said regenerative coupling means, and bias clamping means coupled to said delay line for restoring the bias of said tube between pu ses.

5. A blocking oscillator circuit for producing equally spaced pulses comprising, a tube having at least a grid and an anode, means for regeneratively coupling the grid and anode circuits, a first delay line in said grid circuit, said first delay line being open ended so that a pulse appearing at the grid is delayed and reflected back to the grid for predeterminatively limiting the regeneration and thereby predeterminatively limiting the duration of the pulses, a second delay line in said anode circuit for delaying any pulses appearing at the anode by a second pre-, determined time interval, and means for coupling the output of said second delay line to said grid circuit for initiating regeneration, the duration of said second predetermined interval determining the spacing between successive pulses.

6. Apparatus of claim 3 wherein a phase converting network is coupled to said delay line for improving the frequency response of said delay line.

7. A pulse generator comprising, a blocking oscillator for producing spaced voltage pulses, said blocking oscillator having grid and anode circuits, means coupled to said grid circuit for determining the bias on said grid and thereby the period of conduction of said blocking oscillator and signal storage means coupled to said anode circuit for determining the times of conduction of said blocking oscillator whereby the duration and repetition rate of output pulses from said blocking oscillator are determined.

8. A pulse generator comprising, a blocking oscillator for producing spaced voltage pulses, said blocking oscillator having grid and anode circuits, means for initiating conduction in said blocking oscillator, first voltage storage means coupled to said grid circuit for determining the period of conduction of said blocking oscillator, second voltage storage means coupled to said anode circuit and having a longer time of storage than said first voltage storage and means for coupling the output of said second voltage storage means to said grid to renew conduction in said blocking oscillator.

9. A pulse generator comprising, a blocking oscillator for producing spaced voltage pulses, said blocking oscillator having grid and anode circuits, means for initiating conduction in said blocking oscillator, first storage means coupled to said grid circuit for cutting off conduction in said blocking oscillator after a period T1, second storage means coupled to said anode circuit having a time interval of storage T2, T2 being greater than T1, and means for coupling the output of said second storage means back to said grid circuit to renew conduction in said blocking oscillator after time interval T2 has elapsed.

10. A pulse generator comprising, a blocking oscillator for producing spaced voltage pulses, said blocking oscillator having control grid, anode, and auxiliary grid circuits, means for applying a pulse of relatively long duration to said auxiliary grid to initiate conduction and the production of a pulse in said blocking oscillator, storage means coupled to said control grid circuit for storing said pulse voltage for a relatively short time and thereby maintaining said blocking oscillator in conduction only for said relatively short time, delay means coupled to said anode circuit for storing said pulse voltage for a delay period longer than said relatively short time and shorter than said relatively long time, and means for coupling said pulse voltage back from said delay means to said grid circuit after said delay period has elapsed to renew conduction in said blocking oscillator.

11. A pulse generator comprising, a blocking oscillator for producing spaced voltage pulses, said blocking oscillator having grid and anode circuits, a first delay line I coupled to said grid circuit for determining the duration of output pulses from said blocking oscillator, and a second delay line having a longer delay than said first delay line coupled to said blocking oscillator for determining the repetition rate of output pulses from said blocking oscillator.

12. A pulse generator comprising, a blocking oscillator for producing spaced voltage pulses, said blocking oscillator having grid and anode circuits, a first delay line coupled to said grid circuit for delaying pulses applied thereto for a first period, said delayed pulse being coupled back to said grid circuit after said first period of delay to cut off conduction in said blocking oscillator, a second delay line coupled to said anode circuit for delaying pulses applied thereto for a second period greater than said first period, and means for coupling back pulses from said second delay line after said second period of delay to said grid circuit to renew conduction in said blocking oscillator whereby the duration and repetition rate of pulses from said blocking oscillator are determined.

13. A pulse generator comprising, a blocking oscillator for producing spaced voltage pulses, said blocking oscillator having anode, control grid, and auxiliary grid circuits, bias means coupled to said control grid and to said auxiliary grid for maintaining said blocking oscillator normally nonconductive, means for coupling a first voltage pulse of relatively long duration to said auxiliary grid, means for simultaneously coupling a second voltage pulse of relatively short duration to said control grid, said first and second voltage pulses initiating conduction and the production of a third voltage pulse by said blocking oscillator, a delay line coupled to said anode circuit and energized therefrom by said third voltage pulse, an electron tube having input and output circuits, a resistor connected to said input circuit, said input circuit and said resistor terminating said delay line in an impedance greater than its characteristic impedance, said electron tube being triggered by said third voltage pulse after said third voltage pulse traverses said delay line, the time of said traversing being greater than the duration of said third voltage pulse, and a condenser connected in series relationship with said electron tube and said control grid bias means, conduction of said electron tube permitting discharge of said condenser therethrough thereby maintaining said control grid at a steady bias value between periods of conduction of said blocking oscillator.

14. In a pulse generating system for producing in response to a single gating pulse a sequence of precisely timed output pulses of predetermined duration, the combination of, a blocking oscillator having anode, control grid and auxiliary grid circuits, means for biasing said control grid and auxiliary grid circuits whereby said blocking oscillator is normally maintained inoperative, a source of relatively long gating pulses, means for feeding said gating pulses and complementary trigger pulses to said control and auxiliary grid circuits to unblock the oscillator and thereby generate substantially rectangular output pulses, a delay line associated with said anode circuit and adapted to be supplied with said output pulses, a discharge device eifectively terminating said delay line, a condenser connected in series relationship with said discharge de-.

vice and said control grid bias means whereby said output pulses after traversing said delay line will render said discharge device conductive to discharge said condenser therethrough and re-establish the steady state blocking bias condition on the control grid of the blocking oscillator.

15. A pulse forming arrangement as defined in claim 14 wherein the terminating impedance of the delay line exceeds its characteristic value whereby the output pulses will be reflected back toward the anode circuit of the blocking oscillator after traversing said delay line.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,212,420 Harnett Aug. 20, 1940 2,266,154 Blumlein Dec. 16, 1941 2,410,523 Rankin Nov. 5, 1946 2,444,782 Lord July 6, 1948 2,447,082 Miller Aug. 17, 1948 2,506,335 Bias May 2, 1950 2,564,000

Gafiney Aug. 14, 1951 

